The invention pertains to methods of forming layers of particulates on substrates, to methods of forming field emission emitter tips, and to associated apparatuses.
Field emitters are widely used in display devices. An exemplary display device is a flat panel display. Clarity, or resolution, of a field emission display is a function of a number of factors, including emitter tip sharpness. Specifically, sharper emitter tips can produce higher resolution displays than less sharp emitter tips. Accordingly, numerous methods have been proposed for fabrication of very sharp emitter tips (i.e., emitter tips having tip radii of 100 nanometers or less). Fabrication of very sharp tips has, however, proved difficult. It has proved particularly difficult to build large areas of sharp emitter tips using photolithography while maintaining resolution and stringent dimensional control over large area substrates used for display manufacture. In light of these difficulties, it would be desirable to develop alternative methods of forming emitter tips. Several methods have been proposed. Some utilize deposited particulates to form a non-photolithographic etch mask. A subsequent etching step, or series of steps, then forms emitter tips. The use of deposited particulates on a substrate as an etch mask can reduce complexity of an etching process and improve sharpness of emitter tips relative to photolithographic processing. It would, therefore, be desirable to develop alternative methods for utilizing deposited materials in etch masking processes.
In other aspects of the prior art, it is frequently desired to form uniform layers of particulates on substrates. Such can occur through, for example, Langmuir-Blodgett technologies. It would be desirable to develop methods and apparatuses for automating formation of uniform layers of particulates on substrates.
In one aspect, the invention encompasses a method of forming a layer of particulates on a substrate. A first substrate is fastened to a second substrate. While the first substrate is fastened to the second substrate, at least a portion of the first substrate is submerged in a liquid. Particulates are suspended on an upper surface of the liquid. The submerged first substrate is moved relative to the suspended particulates to form a layer of the particulates supported on the first substrate. The first substrate is subsequently removed from the second substrate.
In another aspect, the invention encompasses another method of forming a layer on a substrate. A liquid is provided in a vessel and particulates are suspended on an upper surface of the liquid. A pusher bar is provided to compress the particulates against one another. A conveyor having substrates fastened thereto is provided. The conveyor is drawn into the liquid and upwardly through the suspended particulates. The substrate is drawn upwardly through the suspended particulates with the conveyor. As the substrate is drawn upwardly, the suspended particulates adhere to it to form a layer of the particulates supported on the substrate.
In yet another aspect, the invention encompasses a layer forming apparatus. The apparatus comprises a vessel configured to retain a liquid, and a pusher bar joined to the vessel and configured to compress particulates on an upper surface of the liquid. The apparatus further comprises a conveyor which enters and exits the vessel. The conveyor is configured to removably retain substrates and to transport such substrates through the vessel. The vessel, conveyor and pusher bar are configured to form a layer of the particulates on substrates as the substrates are transported through the vessel by the conveyor.